As shown in FIG. 27, a continuous unloader generally includes upper sprockets a, lower sprockets b that are located below the upper sprockets a, front sprockets c that are located in front of the lower sprockets b, and an endless bucket conveyer d that is circularly engaged with the sprockets a, b, c. Bulk cargo f (such as coal, iron ore) in a ship hold e is dug up by the bucket conveyer d between the front sprockets c and the lower sprockets b and the dug cargo is lifted up by the bucket conveyer d between the lower sprockets b and the upper sprockets a. The buckets are then turned over by reverse sprockets g such that the cargo in the buckets is dropped on a table feeder (not shown) provided in a top support frame h. The dropped cargo is carried by a conveyer (not shown) and a chute j that are provided in a beam i and is unloaded onto a quay k.
As the opening width of a hatch m of the ship hold e is generally narrower than the inner width of the ship hold e, it is convenient if the front sprockets c and the lower sprockets b can be arranged such that the distance between them is narrowed when they pass through the hatch m and then the distance is widened when they dig up the cargo in the ship hold e. An example of such a continuous unloader that is capable of adjusting the distance between the front sprockets c and the lower sprockets b is shown in FIG. 28.
In the continuous unloader shown in FIG. 28, the front sprockets c are mounted at one end of a telescopically extensible/retractable frame q and the lower sprockets b are mounted at the other end of the extensible frame q such that the distance between the both sprockets c, b can be changed by an extensible/retractable cylinder r. The extensible (/retractable) frame q includes an inner cylinder o and an outer cylinder p. A guide rod t that is connected with the outer cylinder p by way of a connection member s is engaged with a guide channel u that is provided at the lower end of a frame (an elevator casing) n for supporting the upper sprockets a such that the guide rod t can be vertically moved along the guide channel u by a up-down cylinder v. The distance between the outer cylinder p and the upper sprockets a can be changed by extending/retracting the up-down cylinder v.
According to the arrangement described above, the distance between the front sprockets c and the lower sprockets b can be narrowed without generating too much slack in chains w of the bracket conveyer d by retracting the extensible/retractable cylinder r and extending the up-down cylinder v. Conversely, the distance between the front sprockets c and the lower sprockets b can be widened without generating too much tense in the chains w of the bracket conveyer d by extending the extensible/retractable cylinder r and retracting the up-down cylinder v.
However, the conventional continuous unloader described above has following shortcomings.
First, as two cylinders (the extensible/retractable cylinder r and the up-down cylinder v) are needed for adjusting the distance between the front sprockets c and the lower sprockets b, the structure of the whole system becomes complicated. In addition, as extension/retraction of the extensible/retractable cylinder r and the retraction/extension of the up-down cylinder v must be synchronized such that no excessive slack or tense be generated in the chains w of the bucket conveyer d during the extension/retraction or up/down motion of the extensible frame q, a complicated hydraulic control is required.
Further, as the extensible/retractable cylinder r must have a relatively long and large special cylinder that has the same length of stroke as the extension/retraction stroke of the extensible frame q, the extensible/retractable cylinder r inevitably has a large size and volume, increasing its production cost. Further, since the up-down cylinder v is arranged such that it lifts up the extensible frame q with the extensible/retractable cylinder r, the up-down cylinder v is required to have a lift-up force sufficient for lifting up the extensible/retractable cylinder r as well. This results in the larger size of the up-down cylinder v and the whole system.
The present invention is contrived in order to solve the problems described above. Its object is to propose a continuous unloader that has a simple structure and a relatively small weight in which no complicated control is required and the production cost is relatively low.